Technique for the growth of planar semi-polar gallium nitride

ABSTRACT

A method for growing planar, semi-polar nitride film on a miscut spinel substrate, in which a large area of the planar, semi-polar nitride film is parallel to the substrate&#39;s surface. The planar films and substrates are: (1) {10 1 1} gallium nitride (GaN) grown on a {100} spinel substrate miscut in specific directions, (2) {10 1 3} gallium nitride (GaN) grown on a {110} spinel substrate, (3) {11 2 2} gallium nitride (GaN) grown on a {1 1 00} sapphire substrate, and (4) {10 1 3} gallium nitride (GaN) grown on a {1 1 00} sapphire substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 35 U.S.C. §120 of co-pendingand commonly-assigned U.S. Utility patent application Ser. No.12/697,961, filed on Feb. 1, 2010, by Troy J. Baker, Benjamin A.Haskell, Paul T. Fini, Steven P. DenBaars, James S. Speck, and ShujiNakamura, entitled “TECHNIQUE FOR THE GROWTH OF PLANAR SEMI-POLARGALLIUM NITRIDE,” which application is a continuation under 35 U.S.C.§120 of U.S. Utility patent application Ser. No. 11/621,482, filed onJan. 9, 2007, now U.S. Pat. No. 7,704,331, issued Apr. 27, 2010, by TroyJ. Baker, Benjamin A. Haskell, Paul T. Fini, Steven P. DenBaars, JamesS. Speck, and Shuji Nakamura, entitled “TECHNIQUE FOR THE GROWTH OFPLANAR SEMI-POLAR GALLIUM NITRIDE,” which application is a continuationunder 35 U.S.C. §120 of U.S. Utility patent application Ser. No.11/372,914, filed on Mar. 10, 2006, now U.S. Pat. No. 7,220,324, issuedon May 22, 2007, by Troy J. Baker, Benjamin A. Haskell, Paul T. Fini,Steven P. DenBaars, James S. Speck, and Shuji Nakamura, entitled“TECHNIQUE FOR THE GROWTH OF PLANAR SEMI-POLAR GALLIUM NITRIDE,” whichapplication claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application Ser. No. 60/660,283, filed on Mar. 10,2005, by Troy J. Baker, Benjamin A. Haskell, Paul T. Fini, Steven P.DenBaars, James S. Speck, and Shuji Nakamura, entitled “TECHNIQUE FORTHE GROWTH OF PLANAR SEMI-POLAR GALLIUM NITRIDE;” all of whichapplications are incorporated by reference herein.

This application is related to the following co-pending andcommonly-assigned applications:

U.S. Provisional Patent Application Ser. No. 60/686,244, filed on Jun.1, 2005, by Robert M. Farrell, Troy J. Baker, Arpan Chakraborty,Benjamin A. Haskell, P. Morgan Pattison, Rajat Sharma, Umesh K. Mishra,Steven P. DenBaars, James S. Speck, and Shuji Nakamura, entitled“TECHNIQUE FOR THE GROWTH AND FABRICATION OF SEMIPOLAR (Ga,Al,In,B)NTHIN FILMS, HETEROSTRUCTURES, AND DEVICES;”

U.S. Provisional Patent Application Ser. No. 60/698,749, filed on Jul.13, 2005, by Troy J. Baker, Benjamin A. Haskell, James S. Speck, andShuji Nakamura, entitled “LATERAL GROWTH METHOD FOR DEFECT REDUCTION OFSEMIPOLAR NITRIDE FILMS;”

U.S. Provisional Patent Application Ser. No. 60/715,491, filed on Sep.9, 2005, by Michael Iza, Troy J. Baker, Benjamin A. Haskell, Steven P.DenBaars, and Shuji Nakamura, entitled “METHOD FOR ENHANCING GROWTH OFSEMIPOLAR (Al, In,Ga,B)N VIA METALORGANIC CHEMICAL VAPOR DEPOSITION;”

U.S. Provisional Patent Application Ser. No. 60/760,739, filed on Jan.20, 2006, by John F. Kaeding, Michael Iza, Troy J. Baker, Hitoshi Sato,Benjamin A. Haskell, James S. Speck, Steven P. DenBaars, and ShujiNakamura, entitled “METHOD FOR IMPROVED GROWTH OF SEMIPOLAR(Al,In,Ga,B)N;”

U.S. Provisional Patent Application Ser. No. 60/760,628, filed on Jan.20, 2006, by Hitoshi Sato, John F. Keading, Michael Iza, Troy J. Baker,Benjamin A. Haskell, Steven P. DenBaars, and Shuji Nakamura, entitled“METHOD FOR ENHANCING GROWTH OF SEMIPOLAR (Al,In,Ga,B)N VIA METALORGANICCHEMICAL VAPOR DEPOSITION;”

U.S. Provisional Patent Application Ser. No. 60/772,184, filed on Feb.10, 2006, by John F. Kaeding, Hitoshi Sato, Michael Iza, HirokuniAsamizu, Hong Zhong, Steven P. DenBaars, and Shuji Nakamura, entitled“METHOD FOR CONDUCTIVITY CONTROL OF SEMIPOLAR (Al,In,Ga,B)N;”

U.S. Provisional Patent Application Ser. No. 60/774,467, filed on Feb.17, 2006, by Hong Zhong, John F. Kaeding, Rajat Sharma, James S. Speck,Steven P. DenBaars, and Shuji Nakamura, entitled “METHOD FOR GROWTH OFSEMIPOLAR (Al,In,Ga,B) N OPTOELECTRONICS DEVICES;”

U.S. Utility patent application Ser. No. 10/537,644, filed Jun. 6, 2005,by Benjamin A. Haskell, Michael D. Craven, Paul T. Fini, Steven P.DenBaars, James S. Speck, and Shuji Nakamura, entitled “GROWTH OFREDUCED DISLOCATION DENSITY NON-POLAR GALLIUM NITRIDE BY HYDRIDE VAPORPHASE EPITAXY,” which application claims the benefit under 35 U.S.C.Section 365(c) of International Patent Application No. PCT/US03/21918,filed Jul. 15, 2003, by Benjamin A. Haskell, Michael D. Craven, Paul T.Fini, Steven P. DenBaars, James S. Speck, and Shuji Nakamura, entitled“GROWTH OF REDUCED DISLOCATION DENSITY NON-POLAR GALLIUM NITRIDE BYHYDRIDE VAPOR PHASE EPITAXY,” which application claims the benefit under35 U.S.C. Section 119(e) of U.S. Provisional Patent Application Ser. No.60/433,843, filed Dec. 16, 2002, by Benjamin A. Haskell, Michael D.Craven, Paul T. Fini, Steven P. DenBaars, James S. Speck, and ShujiNakamura, entitled “GROWTH OF REDUCED DISLOCATION DENSITY NON-POLARGALLIUM NITRIDE BY HYDRIDE VAPOR PHASE EPITAXY;”

U.S. Utility patent application Ser. No. 10/537,385, filed Jun. 3, 2005,by Benjamin A. Haskell, Paul T. Fini, Shigemasa Matsuda, Michael D.Craven, Steven P. DenBaars, James S. Speck, and Shuji Nakamura, entitled“GROWTH OF PLANAR, NON-POLAR A-PLANE GALLIUM NITRIDE BY HYDRIDE VAPORPHASE EPITAXY,” which application claims the benefit under 35 U.S.C.Section 365(c) of International Patent Application No. PCT/US03/21916,filed Jul. 15, 2003, by Benjamin A. Haskell, Paul T. Fini, ShigemasaMatsuda, Michael D. Craven, Steven P. DenBaars, James S. Speck, andShuji Nakamura, entitled “GROWTH OF PLANAR, NON-POLAR A-PLANE GALLIUMNITRIDE BY HYDRIDE VAPOR PHASE EPITAXY,” which application claims thebenefit under 35 U.S.C. Section 119(e) of U.S. Provisional PatentApplication Ser. No. 60/433,844, filed Dec. 16, 2002, by Benjamin A.Haskell, Paul T. Fini, Shigemasa Matsuda, Michael D. Craven, Steven P.DenBaars, James S. Speck, and Shuji Nakamura, entitled “TECHNIQUE FORTHE GROWTH OF PLANAR, NON-POLAR A-PLANE GALLIUM NITRIDE BY HYDRIDE VAPORPHASE EPITAXY;”

U.S. Utility patent application Ser. No. 10/413,691, filed Apr. 15,2003, by Michael D. Craven and James S. Speck, entitled “NON-POLARA-PLANE GALLIUM NITRIDE THIN FILMS GROWN BY METALORGANIC CHEMICAL VAPORDEPOSITION,” which application claims the benefit under 35 U.S.C.Section 119(e) of U.S. Provisional Patent Application Ser. No.60/372,909, filed Apr. 15, 2002, by Michael D. Craven, Stacia Keller,Steven P. DenBaars, Tal Margalith, James S. Speck, Shuji Nakamura, andUmesh K. Mishra, entitled “NON-POLAR GALLIUM NITRIDE BASED THIN FILMSAND HETEROSTRUCTURE MATERIALS;”

U.S. Utility patent application Ser. No. 10/413,690, filed Apr. 15,2003, by Michael D. Craven, Stacia Keller, Steven P. DenBaars, TalMargalith, James S. Speck, Shuji Nakamura, and Umesh K. Mishra, entitled“NON-POLAR (Al,B,In,Ga)N QUANTUM WELL AND HETEROSTRUCTURE MATERIALS ANDDEVICES, which application claims the benefit under 35 U.S.C. Section119(e) of U.S. Provisional Patent Application Ser. No. 60/372,909, filedApr. 15, 2002, by Michael D. Craven, Stacia Keller, Steven P. DenBaars,Tal Margalith, James S. Speck, Shuji Nakamura, and Umesh K. Mishra,entitled “NON-POLAR GALLIUM NITRIDE BASED THIN FILMS AND HETEROSTRUCTUREMATERIALS;”

U.S. Utility patent application Ser. No. 10/413,913, filed Apr. 15,2003, by Michael D. Craven, Stacia Keller, Steven P. DenBaars, TalMargalith, James S. Speck, Shuji Nakamura, and Umesh K. Mishra, entitled“DISLOCATION REDUCTION IN NON-POLAR GALLIUM NITRIDE THIN FILMS,” whichapplication claims the benefit under 35 U.S.C. Section 119(e) of U.S.Provisional Patent Application Ser. No. 60/372,909, filed Apr. 15, 2002,by Michael D. Craven, Stacia Keller, Steven P. DenBaars, Tal Margalith,James S. Speck, Shuji Nakamura, and Umesh K. Mishra, entitled “NON-POLARGALLIUM NITRIDE BASED THIN FILMS AND HETEROSTRUCTURE MATERIALS;”

International Patent Application No. PCT/US03/39355, filed Dec. 11,2003, by Michael D. Craven and Steven P. DenBaars, entitled “NONPOLAR(Al, B, In, Ga)N QUANTUM WELLS,” which application is acontinuation-in-part of the above-identified Patent Application Nos.PCT/US03/21918, PCT/US03/21916, Ser. No. 10/413,691, Ser. No.10/413,690, Ser. No. 10/413,913;

all of which applications are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for the growth of planarsemi-polar gallium nitride.

2. Description of the Related Art

The usefulness of gallium nitride (GaN), and its ternary and quaternarycompounds incorporating aluminum and indium (AlGaN, InGaN, AlInGaN), hasbeen well established for fabrication of visible and ultravioletoptoelectronic devices and high-power electronic devices. These devicesare typically grown epitaxially using growth techniques includingmolecular beam epitaxy (MBE), metalorganic chemical vapor deposition(MOCVD), and hydride vapor phase epitaxy (HVPE).

GaN and its alloys are most stable in the hexagonal würtzite crystalstructure, in which the structure is described by two (or three)equivalent basal plane axes that are rotated 120° with respect to eachother (the a-axes), all of which are perpendicular to a unique c-axis.Group III and nitrogen atoms occupy alternating c-planes along thecrystal's c-axis. The symmetry elements included in the würtzitestructure dictate that III-nitrides possess a bulk spontaneouspolarization along this c-axis, and the würtzite structure exhibitspiezoelectric polarization.

Current nitride technology for electronic and optoelectronic devicesemploys nitride films grown along the polar c-direction. However,conventional c-plane quantum well structures in III-nitride basedoptoelectronic and electronic devices suffer from the undesirablequantum-confined Stark effect (QCSE), due to the existence of strongpiezoelectric and spontaneous polarizations. The strong built-inelectric fields along the c-direction cause spatial separation ofelectrons and holes that in turn give rise to restricted carrierrecombination efficiency, reduced oscillator strength, and red-shiftedemission.

One approach to eliminating the spontaneous and piezoelectricpolarization effects in GaN optoelectronic devices is to grow thedevices on non-polar planes of the crystal. Such planes contain equalnumbers of Ga and N atoms and are charge-neutral. Furthermore,subsequent non-polar layers are equivalent to one another so the bulkcrystal will not be polarized along the growth direction. Two suchfamilies of symmetry-equivalent non-polar planes in GaN are the {11 20}family, known collectively as a-planes, and the {1 100} family, knowncollectively as m-planes. Unfortunately, despite advances made byresearchers at the University of California, for example, as describedin the applications cross-referenced above, growth of non-polar GaNremains challenging and has not yet been widely adopted in theIII-nitride industry.

Another approach to reducing or possibly eliminating the polarizationeffects in GaN optoelectronic devices is to grow the devices onsemi-polar planes of the crystal. The term “semi-polar planes” can beused to refer to a wide variety of planes that possess both two nonzeroh, i, or k Miller indices and a nonzero 1 Miller index. Some commonlyobserved examples of semi-polar planes in c-plane GaN heteroepitaxyinclude the {11 22}, {10 11}, and {10 13} planes, which are found in thefacets of pits. These planes also happen to be the same planes that theinventors have grown in the form of planar films. Other examples ofsemi-polar planes in the würtzite crystal structure include, but are notlimited to, {10 12}, {20 21}, and {10 14}. The nitride crystal'spolarization vector lies neither within such planes or normal to suchplanes, but rather lies at some angle inclined relative to the plane'ssurface normal. For example, the {10 11} and {10 13} planes are at62.98° and 32.06° to the c-plane, respectively.

The other cause of polarization is piezoelectric polarization. Thisoccurs when the material experiences a compressive or tensile strain, ascan occur when (Al, In, Ga, B)N layers of dissimilar composition (andtherefore different lattice constants) are grown in a nitrideheterostructure. For example, a thin AlGaN layer on a GaN template willhave in-plane tensile strain, and a thin InGaN layer on a GaN templatewill have in-plane compressive strain, both due to lattice matching tothe GaN. Therefore, for an InGaN quantum well on GaN, the piezoelectricpolarization will point in the opposite direction than that of thespontaneous polarization of the InGaN and GaN. For an AlGaN layerlatticed matched to GaN, the piezoelectric polarization will point inthe same direction as that of the spontaneous polarization of the AlGaNand GaN.

The advantage of using semi-polar planes over c-plane nitrides is thatthe total polarization will be reduced. There may even be zeropolarization for specific alloy compositions on specific planes. Suchscenarios will be discussed in detail in future scientific papers. Theimportant point is that the polarization will be reduced compared tothat of c-plane nitride structures.

Bulk crystals of GaN are not available, so it is not possible to simplycut a crystal to present a surface for subsequent device regrowth.Commonly, GaN films are initially grown heteroepitaxially, i.e. onforeign substrates that provide a reasonable lattice match to GaN.

Semi-polar GaN planes have been demonstrated on the sidewalls ofpatterned c-plane oriented stripes. Nishizuka et al. have grown {11 22}InGaN quantum wells by this technique. (See Nishizuka, K., AppliedPhysics Letters, Vol. 85, No. 15, Oct. 11, 2004.) They have alsodemonstrated that the internal quantum efficiency of the semi-polarplane {11 22} is higher than that of the c-plane, which results from thereduced polarization.

However, this method of producing semi-polar planes is drasticallydifferent than that of the present invention; it is an artifact fromepitaxial lateral overgrowth (ELO). ELO is used to reduce defects in GaNand other semiconductors. It involves patterning stripes of a maskmaterial, often SiO₂ for GaN. The GaN is grown from open windows betweenthe mask and then grown over the mask. To form a continuous film, theGaN is then coalesced by lateral growth. The facets of these stripes canbe controlled by the growth parameters. If the growth is stopped beforethe stripes coalesce, then a small area of semi-polar plane can beexposed. The surface area may be 10 μm wide at best. Moreover, thesemi-polar plane will be not parallel to the substrate surface. Inaddition, the surface area is too small to process into a semi-polarLED. Furthermore, forming device structures on inclined facets issignificantly more difficult than forming those structures on normalplanes.

The present invention describes a technique for the growth of planarfilms of semi-polar nitrides, in which a large area of (Al, In, Ga)N isparallel to the substrate surface. For example, samples are often grownon 10 mm×10 mm or 2 inch diameter substrates compared to the fewmicrometer wide areas previously demonstrated for the growth ofsemi-polar nitrides.

SUMMARY OF THE INVENTION

The present invention describes a method for growing semi-polar nitridesas planar films, such as {10 11}, {10 13}, and {11 22} planar films ofGaN. Growth of semi-polar nitride semiconductors offer a means ofreducing polarization effects in würtzite-structure III-nitride devicestructures.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIGS. 1A, 1B and 1C are optical micrographs of GaN on (100) spinel withsubstrate miscuts of FIG. 1A (no miscut), FIG. 1B (miscut in <010>), andFIG. 1C (miscut in <011>).

FIG. 2 is a flowchart illustrating the process steps of the preferredembodiment of the present invention.

FIG. 3 is a photograph of an LED grown by MOCVD on a {10 11} GaNtemplate grown by HYPE.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

Overview

Growth of semi-polar nitride semiconductors, for example, {10 11}, {1013} and {11 22} planes of GaN, offer a means of reducing polarizationeffects in wiirtzite-structure III-nitride device structures. Thesemiconductor term nitrides refers to (Ga,Al,In,B)N and any alloycomposition of these semiconductors. Current nitride devices are grownin the polar [0001] c-direction, which results in charge separationalong the primary conduction direction in vertical devices. Theresulting polarization fields are detrimental to the performance ofcurrent state of the art optoelectronic devices. Growth of these devicesalong a semi-polar direction could improve device performancesignificantly by reducing built-in electric fields along the conductiondirection.

Until now, no means existed for growing large area, high quality filmsof semi-polar nitrides suitable for use as device layers, templates, orsubstrates in device growth. The novel feature of this invention is theestablishment that semi-polar nitrides can be grown as planar films. Asevidence, the inventors have grown {10 11}, {10 13}, and {11 22} planarfilms of GaN. However, the scope of this idea is not limited to solelythese examples. This idea is relevant to all semi-polar planar films ofnitrides.

Technical Description

The present invention comprises a method for growing planar nitridefilms in which a large area of the semi-polar nitrides is parallel to asubstrate surface. Examples of this are {10 11} and {10 13} GaN films.In this particular embodiment, MgAl₂O₄ spinel substrates are used in thegrowth process. It is critically important that the spinel is miscut inthe proper direction for growth of {10 11} GaN. {10 11} GaN grown on{100} spinel that is on-axis and that is miscut toward the <001>direction will have two domains at 90° to each other. This is apparentin the optical micrographs of GaN on (100) spinel shown in FIG. 1A (nomiscut) and FIG. 1B (a miscut in <010>), respectively.

However, {10 11} single crystal GaN grows on {100} spinel that is miscutin the <011>, as shown in the optical micrograph of GaN on (100) spinelin FIG. 1C (a miscut in <011>) X-ray diffraction (XRD) was used toverify that the films grown on (100) spinel with miscut toward <011>direction are single crystal and that the films grown on-axis or miscuttoward <010> direction have two domains.

{10 13} single crystal GaN was grown on nominally on-axis (lacking anintentional miscut) {110} spinel. XRD was used to verify that the {1013} GaN is single crystal.

Also, planar films of {11 22} GaN and {10 13} GaN have been grown onm-plane sapphire, {1 100} Al₂O₃. It is uncommon in semiconductor growthfor one substrate to be used for growth of two distinct planes of thesame epitaxial material. However, the plane can be reproducibly selectedby flowing ammonia at different temperatures before the GaN growth.Again, XRD was used to confirm the single crystal character of thefilms.

Thus, there has been experimentally proven four examples of planarsemi-polar nitride films:

1) {10 11} GaN on {100} spinel miscut in specific directions (<001>,<010> and <011>),

2) {10 13} GaN on {110} spinel,

3) {11 22} GaN on {1 100} sapphire, and

4) {10 13} GaN on {1 100} sapphire.

These films were grown using an HVPE system in Shuji Nakamura's lab atthe University of California, Santa Barbara. A general outline of growthparameters for both {10 11} and {10 13} is a pressure between 10 torrand 1000 torr, and a temperature between 900° C. and 1200° C. This widerange of pressure shows that these planes are very stable when growingon the specified substrates. The epitaxial relationships should holdtrue regardless of the type of reactor. However, the reactor conditionsfor growing these planes will vary according to individual reactors andgrow methods (HVPE, MOCVD, and MBE, for example).

Process Steps

FIG. 2 is a flowchart illustrating the process steps of the preferredembodiment of the present invention. Specifically, these process stepscomprise a method for growing planar, semi-polar nitride films in whicha large area of the planar, semi-polar nitride film is parallel to thesubstrate's surface.

Block 10 represents the optional step of preparing the substrate. Forexample, the preparation may involve performing a miscut of thesubstrate. For the growth of {10 11} GaN, a (100) spinel substrate isused with a miscut in the <011> direction (which includes <010> and<011>). For the growth of {10 13} GaN, an on-axis (110) spinel substrateis used. The (110) spinel may or may not have a miscut in any direction,but a miscut is not necessary as it is to grow {10 11} GaN on (100)spinel.

Block 12 represents the step of loading the substrate into an HVPEreactor. The reactor is evacuated to at least 9E-2 torr to removeoxygen, then it is backfilled with nitrogen.

Block 14 represents the step of turning on the furnace and ramping thetemperate of the reactor under conditions to encourage nitridization ofthe surface of the substrate.

Block 16 represents the step of performing a gas flow. The processgenerally flows nitrogen, hydrogen, and/or ammonia over the substrate atatmospheric pressure.

Block 18 represents the step of reducing the pressure in the reactor.The furnace setpoint is 1000° C., and when it reaches this temperature,the pressure of the reactor is reduced to 62.5 torr.

Block 20 represents the step of performing a GaN growth. After thepressure is reduced, the ammonia flow is set to 1.0 slpm (standardliters per minute), and HCl (hydrogen chloride) flow over Ga (gallium)of 75 sccm (standard cubic centimeters per minute) is initiated to startthe growth of GaN.

Block 22 represents the step of cooling down the reactor. After 20 to 60minutes of GaN growth time, the HCl flow is stopped, and the reactor iscooled down while flowing ammonia to preserve the GaN film.

The end result of these steps comprises a planar, semi-polar nitridefilm in which a large surface area (at least 10 mm×10 mm or a 2 inchdiameter) of the planar, semi-polar nitride film is parallel to thesubstrate's surface.

Although the process steps are described in conjunction with a spinelsubstrate, m-plane sapphire can be used to grow either {11 22} GaN or{10 13} GaN. The process is the same as described above, with oneexception. For growth of {11 22} GaN, ammonia is flowed while thefurnace is ramping to the growth temperature, thus the nitridationoccurs at low temperature. To select for {10 13} GaN, only hydrogen andnitrogen can be flowed during the ramp temperature step. The substrateshould then be subjected to a high temperature nitridation with ammoniaflow at the growth temperature.

After the semi-polar film has been grown using the HVPE system, Block 22represents the step of growing device layers on the substrate usingMOCVD or MBE. This step usually involves doping the nitride layers withn-type and p-type, and growing one or several quantum wells in theregrowth layer. An LED can be made in this step using standard LEDprocessing methods in a cleanroom.

FIG. 3 is a photograph of a green LED grown by MOCVD on a {10 11} GaNtemplate grown by HVPE. Specifically, the template was grown by thepreviously described HVPE growth process, and the LED structure wasgrown by MOCVD. This is the first {10 11} GaN LED.

Crystal Quality (Taken from References [3] and [6])

ω rocking curves were performed to measure crystal quality of a (10 1 1)GaN film on a spinel substrate. The full width at half maximum (FWHM)was measured for the on-axis peaks, rocking in both the GaN[0002] and [1210] directions. The FWHM of the (10 1 1) peak rocking toward theGaN[0002] was 0.7° and the FWHM rocking toward the GaN[1 210] was 1.3°.This shows anisotropy of mosaic in the on-axis rocking curves, as wasobserved in nonpolar m-plane and a-plane GaN films. In skew geometry,the FWHM of the (0002)GaN peak was 3.2°.

The defect structure of a (10 1 1) GaN film on a spinel substrate wasanalyzed using transmission electron microscopy (TEM). Basal planestacking faults (SFs) were observed with a density of 2×10⁵ cm⁻¹.Threading dislocations (TDs) were observed with a density of 2×10⁹ cm⁻².The TD line directions were predominantly in the <10 10> directions onthe (0001) plane.

ω rocking curves were performed to measure crystal quality of a (10 13)GaN film on a spinel substrate. The FWHM of a GaN(10 13) rocking curve,rocking toward the GaN[0002] was 900 arcsec and rocking toward the GaN[1210] was 750 arcsec. In skew geometry, at Ψ=32.0°, the FWHM of the(0002)GaN peak was 880 arcsec.

The SF density and TD density and character are approximately equal for(10 13) and (10 1 1) films. Furthermore, these densities are comparableto results for m- and a-plane GaN films grown by HVPE, MOCVD, and MBE.

For a 10 13 GaN film on a sapphire substrate, the dislocation densitywas observed with a density of 9×10⁸ cm⁻².

Possible Modifications and Variations

The scope of this invention covers more than just the particularexamples cited. This idea is pertinent to all nitrides on any semi-polarplane. For example, one could grow {10 11} AlN, InN, AlGaN, InGaN, orAlInN on a miscut (100) spinel substrate. Another example is that onecould grow {10 12} nitrides, if the proper substrate is found. Theseexamples and other possibilities still incur all of the benefits ofplanar semi-polar films.

The research that was performed in Shuji Nakamura's Lab at University ofCalifornia, Santa Barbara, was done using HVPE; however, direct grow ofsemi-polar planes of nitrides should be possible using MOCVD and MBE aswell. The epitaxial relations should be the same for most growth method,although it can vary as seen in the example of GaN on m-plane sapphire.For example, an MOCVD grown {10 11} GaN LED could be grown directly onmiscut (100) spinel without an HVPE template. This idea covers anygrowth technique that generates a planar semi-polar nitride film.

The reactor conditions will vary by reactor type and design. The growthdescribed here is only a description of one set of conditions that hasbeen found to be useful conditions for the growth of semi-polar GaN. Itwas also discovered that these films will grow under a wide parameterspace of pressure, temperature, gas flows, etc., all of which willgenerate planar semi-polar nitride film.

There are other steps that could vary in the growth process. Anucleation layer has been found unnecessary for our reactor conditions;however, it may or may not be necessary to use a nucleation layer forother reactors, which is common practice in the growth of GaN films. Ithas also been found that nitridizing the substrate improves surfacemorphology for some films, and determines the actual plane grown forother films. However, this may or may not be necessary for anyparticular growth technique.

Advantages and Improvements

The existing practice is to grow GaN with the c-plane normal to thesurface. This plane has a spontaneous polarization and piezoelectricpolarization which are detrimental to device performance. The advantageof semi-polar over c-plane nitride films is the reduction inpolarization and the associated increase in internal quantum efficiencyfor certain devices.

Non-polar planes could be used to completely eliminate polarizationeffects in devices. However, these planes are quite difficult to grow,thus non-polar nitride devices are not currently in production. Theadvantage of semi-polar over non-polar nitride films is the ease ofgrowth. It has been found that semi-polar planes have a large parameterspace in which they will grow. For example, non-polar planes will notgrow at atmospheric pressure, but semi-polar planes have beenexperimentally demonstrated to grow from 62.5 torr to 760 torr, butprobably have an even wider range than that. {1 100} GaN is grown at lowpressure, but when the pressure is increased to 760 torr, all otherthings being equal, c-plane GaN will result. This is probably related tothe outline of the unit cell for the two planes. A further difficulty of{11 20} GaN is In incorporation for InGaN devices. Results have found Inincorporation to be quite favorable for {10 11} GaN.

The advantage of planar semi-polar films over ELO sidewall is the largesurface area that can be processed into an LED or other device. Anotheradvantage is that the growth surface is parallel to the substratesurface, unlike that of ELO sidewall semi-polar planes.

In summary, the present invention establishes that planar semi-polarfilms of nitrides can be grown. This has been experimentally confirmedfor four separate cases. The previously discussed advantages will bepertinent to all planar semi-polar films.

REFERENCES

The following references are incorporated by reference herein:

-   [1] Takeuchi, Tetsuya, Japanese Journal of Applied Physics, Vol. 39,    (2000), pp. 413-416. This paper is a theoretical study of the    polarity of semi-polar GaN films.-   [2] Nishizuka, K., Applied Physics Letters, Vol. 85 No. 15, Oct.    11, 2004. This paper is a study of {11 22} GaN sidewalls of ELO    material.-   [3] T. J. Baker, B. A. Haskell, F. Wu, J. S. Speck, and S, Nakamura,    “Characterization of Planar Semipolar Gallium Nitride Films on    Spinel Substrates,” Japanese Journal of Applied Physics, Vol. 44,    No. 29, (2005), L920.-   [4] A. Chakraborty, T. J. Baker, B. A. Haskell, F. Wu, J. S.    Speck, S. P. Denbaars, S. Nakamura, and U. K. Mishra, “Milliwatt    Power Blue InGaN/GaN Light-Emitting Diodes on Semipolar GaN    Templates,” Japanese Journal of Applied Physics, Vol. 44, No. 30    (2005), L945.-   [5] R. Sharma, P. M. Pattison, H. Masui, R. M. Farrell, T. J.    Baker, B. A. Haskell, F. Wu, S. P. Denbaars, J. S. Speck, and S.    Nakamura, “Demonstration of a Semipolar (10-1-3) InGaN/GaN Green    Light Emitting Diode,” Appl. Phys. Lett. 87, 231110 (2005).-   [6] T. J. Baker, B. A. Haskell, F. Wu, J. S. Speck, and S. Nakamura,    “Characterization of Planar Semipolar Gallium Nitride Films on    Sapphire Substrates,” Japanese Journal of Applied Physics, Vol. 45,    No. 6, (2006), L154.

CONCLUSION

This concludes the description of the preferred embodiment of thepresent invention. The foregoing description of one or more embodimentsof the invention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention be limited not by this detaileddescription, but rather by the claims appended hereto.

What is claimed is:
 1. A device, comprising: a semi-polar III-nitridelayer, wherein: the semi-polar oriented III-nitride layer has a surfacearea of at least 10 mm by 10 mm, the surface area has a semi-polarorientation, and the semi-polar III-nitride layer has a crystal qualitysuitable for subsequent growth of a semi-polar device layer structure onthe surface area.
 2. The device of claim 1, wherein the crystal qualityis such that the surface area has a root mean square surface roughnessof no more than 3.5 nanometers over an area of at least 5 micrometers by5 micrometers.
 3. The device of claim 1, wherein the crystal quality issuch that the surface area has a root mean square surface roughness ofno more than 5.5 nanometers over an area of at least 5 micrometers by 5micrometers.
 4. The device of claim 1, wherein the semi-polarIII-nitride layer comprises Gallium Nitride with the crystal qualitycharacterized by basal plane stacking faults having a density of no morethan 2×10⁵ cm⁻¹.
 5. The device of claim 1, wherein the semi-polarIII-nitride layer comprises Gallium Nitride with the crystal qualitycharacterized by a threading dislocation density of no more than 9×10⁸cm⁻².
 6. The device of claim 1, wherein: the semi-polar III-nitridelayer has the crystal quality characterized by an on-axis rocking curvehaving a peak for the semi-polar orientation with a full width at halfmaximum (FWHM) of: no more than 900 arcseconds for rocking towards a[0002] direction, and no more than 750 arcseconds, for rocking toward a[1-210] direction, and wherein the rocking curve is measured by X-raydiffraction.
 7. The device of claim 1, wherein the semi-polarIII-nitride is single crystal.
 8. The device of claim 1, wherein thesurface area is planar.
 9. The device of claim 1, wherein the surfacearea has a stable semi-polar orientation.
 10. The device of claim 1,wherein the semi-polar oriented III-nitride layer and surface area havea {10-11} orientation.
 11. The device of claim 1, wherein the semi-polaroriented III-nitride layer and the surface area have a {10-13}orientation.
 12. The device of claim 1, wherein the semi-polar orientedIII-nitride layer and the surface area have a {10-14} orientation. 13.The device of claim 1, wherein the semi-polar oriented III-nitride layerand the surface area have a {11-22} orientation.
 14. The device of claim1, wherein the semi-polar oriented III-nitride layer and the surfacearea have a {20-21} orientation.
 15. The device of claim 1, wherein thesemi-polar III-nitride layer is Gallium Nitride.
 16. The device of claim1, wherein the semi-polar III-nitride layer is Aluminum Nitride.
 17. Thedevice of claim 1, wherein the semi-polar III-nitride layer isheteroepitaxially on a foreign substrate.
 18. The device of claim 17,wherein the foreign substrate is sapphire.
 19. The device of claim 17,wherein the foreign substrate is spinel.
 20. The device of claim 1,further comprising a light emitting diode structure deposited on thesurface area.
 21. The device of claim 20, wherein the light emittingdiode structure is a green light emitting diode structure.
 22. Thedevice of claim 1, wherein the semi-polar III-nitride layer reducespolarization in the device layer structure grown on the surface area, ascompared to a device layer structure grown on a c-plane polar nitridefilm, the polarization resulting from the device layer structure and thefilms having dissimilar compositions and therefore different latticeconstants.
 23. A method of fabricating a device, comprising: growing asemi-polar III-nitride layer, wherein: the semi-polar orientedIII-nitride layer has a surface area of at least 10 mm by 10 mm, thesurface area has a semi-polar orientation, and the semi-polarIII-nitride layer is suitable for subsequent growth of a semi-polardevice layer structure on the surface area.
 24. The method of claim 23,wherein growing the semi-polar III-nitride layer comprises: (a) choosinga substrate and an orientation of a surface of the substrate based on adesired semi-polar orientation for the semi-polar III-nitride layer; (b)loading the substrate in a reactor; (c) ramping a temperature of thereactor; and (d) during the ramping, flowing a combination of gases overthe surface of the substrate, wherein: (i) the combination of gasescomprises one or more of ammonia, hydrogen, and nitrogen; and (ii) thecombination of gases is selected based on the substrate and the desiredsemi-polar orientation; and (e) when a growth temperature is reached,growing the semi-polar III-nitride layer on the surface of thesubstrate, using a vapor phase epitaxy or vapor deposition, wherein: agrowth surface of the semi-polar III-nitride layer is planar and stable,and the growth surface of the semi-polar nitride film has the surfacearea of at least 10 mm×10 mm parallel to the surface of the substrate.25. The method of claim 24, wherein: (f) when the substrate is sapphireand the surface is a {1 100} surface of the sapphire, (i) the gas flowscomprise the nitrogen and the hydrogen flowed as the reactor'stemperature is ramped up to the growth temperature, so that the ammoniaflows at the growth temperature, to obtain a planar, semi-polar GaN filmthat is {10 13} GaN, or (ii) the gas flows comprise ammonia flowed asthe reactor's temperature is ramped up to the growth temperature, sothat the ammonia flows at a low temperature, to obtain the planarsemi-polar GaN film that is {11 22} GaN; (g) when the substrate is aspinel substrate and the surface is a {110} surface of the spinel, theramping of the temperature is under conditions to encouragenitridization of the surface of the spinel, to obtain the planarsemi-polar GaN film that is {10 13} GaN; and (h) when the substrate is aspinel substrate and the surface is a {100} surface of the spinel miscutin a <011> direction, the ramping of the temperature is under conditionsto encourage nitridization of the surface of the spinel, to obtain aplanar semi-polar GaN film that is {10 11} GaN.
 26. A device structure,comprising: a semi-polar III-nitride layer, wherein: the semi-polaroriented III-nitride layer has a surface area of at least 10 mm by 10mm, the surface area has a semi-polar orientation, and a III-nitridelight emitting diode (LED) structure deposited on the surface area.